Annotations provide a mechanism for supplementing video with useful information. Annotations can contain, for example, metadata describing the content of the video, subtitles, or additional audio tracks. Annotations can be of various data types, including text, audio, graphics, or other forms. To make their content meaningful, annotations are typically associated with a particular video, or with a particular portion of a video.
One method by which the useful information contained in annotations can be exchanged is by transferring annotated video over a network. However, transferring video content over a network introduces several obstacles. First, video files are generally quite large, and transferring video requires substantial amounts of bandwidth, as well as host and recipient computers that can support the required bandwidth and storage needs. Second, many video files are likely to be copyrighted, or to be otherwise prohibited from distribution without payment of a fee. Compliance with copyright restrictions requires additional software and hardware investments to prevent unauthorized copying. Third, as the recipient of an annotated video may already have an unannotated copy of the video, from a data efficiency perspective the transfer of an annotated copy of the video to such a recipient unnecessarily consumes both bandwidth and storage.
Thus, exchanging annotated video by transferring a complete copy of the video is an inadequate solution.